Engine unit of motorcycle

Abstract

An engine unit of a motorcycle generally include a cylinder head, a cylinder block formed with a cylinder bore therein, a crankcase and a rear case sequentially assembled in this order from a front side of a motorcycle body. A crankshaft is pivoted to a mating face between the cylinder block and the crankcase, a counter shaft which is rotated with the crankshaft in an interlocking manner is pivoted to a mating face between the crankcase and the rear case. These two mating faces lie in planes parallel to each other so as to be substantially perpendicular to a center axis of the cylinder bore of the cylinder block.

What is claimed is:  
     
       1. An engine unit of a motorcycle comprising a cylinder head, a cylinder block formed with a cylinder bore therein, a crankcase and a rear case sequentially assembled in this order from a front side of a motorcycle body, wherein a crankshaft is pivoted to a mating face between the cylinder block and the crankcase, a counter shaft which is rotated with said crankshaft in an interlocking manner is pivoted to a mating face between the crankcase and the rear case and said two mating faces lie in planes parallel to each other so as to be substantially perpendicular to a center axis of the cylinder bore of the cylinder block. 
     
     
       2. An engine unit of a motorcycle according to  claim 1 , wherein said cylinder block is fastened by a fastening member inserted from a side of said rear case so as to extend through the crankcase to thereby commonly fasten said rear case and said crankcase to said cylinder block in a clamping manner. 
     
     
       3. An engine unit of a motorcycle according to  claim 2 , wherein said fastening member has a center axis parallel to the center axis of said cylinder bore. 
     
     
       4. An engine unit of a motorcycle according to  claim 2 , wherein said fastening member includes a plurality of through bolts which are arranged in a vicinity of the crankshaft and the counter shaft so as to clamp the crankshaft and the counter shaft therebetween. 
     
     
       5. An engine unit of a motorcycle according to  claim 4 , wherein said cylinder head is fastened and fixed to the cylinder block by a plurality of long fixing bolts and a single short fixing bolt, and said crankcase and said rear case are fastened and fixed to the cylinder block by the four though bolts and a plurality of fixing bolts. 
     
     
       6. An engine unit of a motorcycle according to  claim 5 , wherein all said fixing bolts have center axes substantially parallel to the center axis of the cylinder bore. 
     
     
       7. An engine unit of a motorcycle according to  claim 1 , wherein the center axis of said cylinder bore is arranged so as to extend substantially along a longitudinal direction of the motorcycle body in a side view thereof and at least one of said cylinder block, crankcase and rear case has a lower portion lowered below a lower surface of the cylinder head so as to provide an inner portion of the lowered portion as an oil storage portion. 
     
     
       8. An engine unit of a motorcycle according to  claim 7 , wherein the center axis of said cylinder bore has an front upward inclination in a side view of the motorcycle body and said oil storage portion has a bottom formed to be flat substantially in parallel to a road surface. 
     
     
       9. An engine unit of a motorcycle according to  claim 8 , wherein said oil storage portion has a front portion to which an oil filter is placed below the cylinder bore in a side view of the motorcycle body and above the bottom of the oil storage portion.